Blasting machining method and blast machining device

ABSTRACT

The disclosure concerns a blasting method achieving antistatic effect and increasing processing amount. In the method, 0.06 cc/min to 150 cc/min, that is, a relatively small amount of liquid is introduced into the blast nozzle and atomized by causing it to strike with the compressed gas flowing through the blast nozzle or the compressed gas ejected from the blast nozzle, and the atomized liquid is ejected together with the compressed gas and the abrasive onto the workpiece. Since the relatively small amount of the atomized liquid is quickly evaporated into water vapor, humidity in a working space is increased, thereby generation of static electricity is prevented. A vaporization heat is absorbed during evaporation then the workpiece is cooled, accordingly, absorption of strike energy from the abrasive due to softening of the surface of the workpiece is prevented, as a result, the processing amount is improved.

TECHNICAL FIELD

The present invention relates to a blasting method in which an abrasiveis ejected together with a compressed gas to perform processes on aworkpiece including cutting, surface polishing, deburring and paintstripping, and also relates to a blasting apparatus for use in theblasting method.

BACKGROUND OF THE INVENTION

Blasting, which uses a cutting force that is exerted when an abrasiveejected together with a compressed gas strikes with a workpiece toprocess the workpiece, is widely used in various applications includingcutting, surface polishing, surface satin finishing, deburring, paintstripping and removal of stains such as rust.

In such blasting, when an abrasive is ejected onto a workpiece togetherwith a compressed gas, static electricity is generated by friction thatis created when the abrasive strikes with the workpiece or friction thatis caused by the strike of the abrasive with interior walls of a cabinetas a working space, causing the ejected abrasive or swarf producedduring cutting of the workpiece to adhere not only to the workpiece andthe interior walls of the cabinet but also to the interior walls of theducts, cyclone, abrasive tank and so on constituting a circulatingsystem for the abrasive. This makes smooth recovery or supply of theabrasive impossible.

In particular, with the increasing demand for microfabrication byblasting, abrasives used are becoming finer and finer. As a result,abrasives are more likely to adhere to the workpiece or the interiorwalls of the cabinet by static electricity and, once attached, they arehard to remove completely by, for example, air blowing. This is onereason for low productivity because there is a need to provide acleaning process after blasting to remove the abrasive adhering to theworkpiece.

One possible way to prevent adhesion of abrasive due to staticelectricity is to provide a voltage-applying static eliminator(“ionizer”) in the blasting apparatus.

However, provision of such an expensive device increases the price ofthe blasting apparatus and thus causes it to lose price competitivenessin the market. In addition, the electrode probes provided in an ionizerto generate ions are easily get dirty and hence need frequentmaintenance. Moreover, because static electricity removal(neutralization) is carried out while the abrasive adheres to theprocessing object, static electricity remains in the areas where theabrasive has been removed.

Further, an ionizer is not structurally suited for use in a blastingapparatus because it performs corona discharge to generate ions and cantherefore be an ignition source for dust explosion and other combustionproblems.

Thus, to solve such a problem caused by static electricity, it has beensuggested that moisture is provided in the working space or thecirculation pathway for the abrasive to eliminate static electricity.

As one example of such a method, it has been suggested that a compressedgas humidified by humidification means is introduced into a blast nozzlefor abrasive ejection to adjust the humidity in the circulating systemfor the abrasive in order to prevent generation of static electricity(See Paragraph [0011] and FIG. 2 in Patent Document 1).

It has been also suggested that an ultrasonic heater or heating is usedto supply water in the form of water vapor to a compressed gas that isintroduced into a blast nozzle for abrasive ejection (See Paragraph[0026] in Patent Document 2).

As a blast nozzle for use in wet blasting designed to prevent dustgeneration, a blast nozzle that mixes a compressed gas, an abrasive(medium) and water in approximately equal amounts in a chamber formedtherein and ejects a three-phase stream consisting of gas, liquid andsolid (abrasive) has been suggested (See Paragraph [0006], FIG. 1, FIG.2 and Table 1[3] in Patent Document 3).

RELATED ARTS Patent Documents Patent Document 1: Japanese Patent No.3846842 Patent Document 2: Japanese Unexamined Patent ApplicationPublication 2011-237378 Patent Document 3: Japanese Unexamined PatentApplication Publication 2006-297568 SUMMARY OF THE INVENTION Problem tobe Solved by the Invention

Among the related arts described above, the blasting method that uses ablast nozzle as described in Patent Document 3, which ejects as large anamount of water as 160 to 200 cc/min (See Table 1 [2] and [3] in PatentDocument 3), is one of the wet blasting methods generally called “wetblasting” or “liquid honing.”

When a workpiece is processed by such a wet blasting method, thegeneration of static electricity can be reduced because the surface ofthe workpiece gets wet with the water ejected.

However, when a workpiece is processed by such a wet blasting method,the surface of the workpiece absolutely gets wet. Thus, such a wetblasting method cannot be applied to a workpiece that should avoidcontact with water, such as a workpiece made of a material that rustseasily. In addition, a washing and drying step are required after theprocessing in some cases, and these processes contribute to lowproductivity.

In addition, in a wet blasting method in which an abrasive is ejectedtogether with a large amount of water as described above, the processingamount (cutting speed or rate) decreases compared to dry blastingbecause the water ejected together with the abrasive absorbs the strikeenergy resulting from the strike of the abrasive with the surface of theworkpiece. When conditions including the material and particle size ofthe abrasive used and the ejection pressure are the same, the processingamount (cut amount) in wet blasting decreases to approximately 1/7 to1/14 of that in dry blasting.

As one example, FIG. 23 and FIG. 24 show the results of measurements ofthe difference in coverage between dry blasting and wet blasting. Theprocessing was performed on a 150 mm square glass plate at an ejectionpressure of 0.3 MPa using an alumina-based abrasive (“FUJIRUNDUM WA#1000” manufactured by Fuji Manufacturing Co., Ltd.) as the abrasive inboth dry and wet blastings.

FIG. 23 shows the changes in processing time until the coverage reaches100% with changes in the distance between a distal end of the blastnozzle and the workpiece (nozzle distance), and FIG. 24 shows thechanges in processing time until the coverage reaches 100% with changesin the particle size of the abrasive. It can be understood that theprocessing time necessary to achieve a coverage of 100% is longer in wetblasting than in dry blasting in all cases.

The term “coverage” as used herein refers to the ratio in percent of atotal indentation area to a processed area. Because the processingamount can be predicted from the degree of coverage, it can beunderstood from FIG. 23 and FIG. 24 that the wet blasting is inferior inprocessing amount (cutting speed) to the dry blasting.

In contrast to the wet blasting described above, in the blasting methoddescribed in Patent Document 1, the humidity in the cabinet as a workingspace is increased by adding moisture to the compressed gas used toeject the abrasive in order to prevent the generation of staticelectricity and the resulting adhesion of the abrasive to the surface ofthe workpiece and the interior walls of the cabinet.

However, in the blasting apparatus described in Patent Document 1, wateris added to the compressed air flowing through a compressed air supplypipe provided between a compressed air supply source and the blastnozzle. Because the compressed air flowing through the compressed airsupply pipe has a lower velocity than the compressed air flowing throughthe small-diameter flow path in the blast nozzle, when water isintroduced into the compressed air supply pipe in a liquid state, it isnot atomized by strike with the compressed air stream and remains in aliquid state, and then is introduced into the blast nozzle, which causesaggregation of the abrasive. This causes clogging of the blast nozzleand results in malfunction of the blasting apparatus.

Thus, although no detailed explanation about the method for adding wateris given in Patent Document 1, when water is added to the compressed airflowing through the compressed air supply pipe, the water must beconverted into water vapor by an ultrasonic or heating method before theaddition to the compressed gas as described in Patent Document 2 toavoid the malfunction caused by such clogging. The need to provide anadditional water addition mechanism that has a function of convertingwater into water vapor as described above makes the apparatuscomplicated in configuration and expensive.

In the methods described in Patent Documents 1 and 2, although water isadded to the compressed gas before it is introduced into the blastnozzle, the fluid that is ejected from the blast nozzle contains no“liquid” because the water is added in the form of water vapor (gas).Thus, the inventions described in Patent Documents 1 and 2 still remainin the category of “dry” blasting in spite of the addition of water.

Thus, the methods described in Patent Documents 1 and 2 have theadvantages of being applicable to a workpiece that should avoid contactwith water as these methods can carry out processing without wetting thesurface of the workpiece and of providing a larger processing amount(cutting speed or rate) than wet blasting.

However, in the blasting methods described in Patent Documents 1 and 2,the generation of static electricity cannot be sufficiently preventedwhen the amount of water supplied is too small to humidify the interiorof the processing chamber sufficiently. On the other hand, when theamount of water supplied is greater than the amount of saturated watervapor, the water condenses in the working space and wets the surface ofthe workpiece and the interior walls of 6 the cabinet. In this case, thegeneration of static electricity can be prevented but the merits of dryblasting are lost.

Thus, in the blasting method described in Patent Document 1, thehumidity in the processing chamber is detected to calculate the amountof water needed before supplying water. The control for it is verycomplicated and makes the apparatus complex in configuration andexpensive.

As described above, the inventions described in Patent Documents 1 and 2still remain in the category of dry blasting and can therefore maintaina larger processing amount (higher cutting speed or rate) than wetblasting, and, at the same time, can overcome the challenge ofpreventing the generation of static electricity. In order to achievethis, however, the adoption of a special apparatus configuration andcomplicated control are indispensable.

On the other hand, as described in Patent Document 3, wet blasting cansignificantly reduce the generation of static electricity with arelatively simple apparatus configuration and without the need forcomplicated control. However, wet blasting requires washing and dryingafter the processing because it wets the workpiece, and the addition ofthese steps lowers its productivity. In addition, because the processingamount (cutting speed or rate) significantly decreases in wet blastingcompared to that in dry blasting, wet blasting is much inferior inmachinability (processing performance) and productivity to dry blastingalso in this respect. Each method has both advantages and disadvantages.

In view of the above, the inventors of the present invention haveconducted intensive studies for the purpose of achieving blasting thatcan prevent the generation of static electricity without sacrificing theprocessing amount and, consequently, have found that the generation ofstatic electricity can be prevented and the processing amount can besignificantly improved by supplying water in an atomized state at aposition immediately upstream of the ejection port of the blast nozzleand limiting the amount of water added to a predetermined range that ismuch smaller than that used in known wet blasting.

In addition, it has been confirmed that the processing amount that canbe obtained by this method is greater than that obtained by wet blastingand, surprisingly, even much greater than that obtained by dry blasting,and some additional effects that cannot be expected from Patent Document1 can be obtained in addition to the improvement in processing amount.

The present invention has been made based on the findings obtained bythe inventors as a result of the intensive studies, and an object of thepresent invention is to provide a blasting method and a blastingapparatus that can be adopted simply by adding minor structural changesto an existing dry blasting apparatus and that not only can prevent thegeneration of static electricity during blasting but also can improvethe processing amount (cutting speed or rate) compared to conventionaldry blasting and even to conventional wet blasting.

Means for Solving the Problems

Means for solving the problems will be described below using referencenumerals used in embodiments of the invention. It is to be noted thatthese reference numerals are only provided for clarifying thecorrespondence relationship between the scope of the claims and theembodiments of the invention, but should not be used for limiting theinterpretation of the technical scope of the claims of the presentinvention.

In order to achieve the above objective, a blasting method according tothe present invention in which an abrasive is ejected together with acompressed gas onto a workpiece W through a blast nozzle 8 comprises thestep of:

introducing a liquid into the blast nozzle 8 and atomizing the liquid bycausing the liquid to contact or strike with the compressed gas flowingthrough the blast nozzle 8 or the compressed gas ejected from the blastnozzle 8, and ejecting the liquid together with the compressed gas andthe abrasive, an amount of the liquid introduced into the blast nozzle 8being 0.06 cc/min to 150 cc/min.

Examples of the liquid may include pure water or hard water whichcontains a scale remover added for scale removal or contains a paint orfluorescent paint added for marking to identify the processed region inaddition to what are called “waters” such as tap water, pure water,purified water and alkali ion water.

In a blasting apparatus 1 according to the present invention for use inthe blasting method as described above, the blasting apparatus 1 forejecting a stream of compressed gas supplied from a compressed gassupply source (not shown) and an abrasive from a blast nozzle 8 as amixed fluid comprises:

a liquid introduction path 88 provided in the blast nozzle 8, having oneend communicable with a liquid supply source (not shown) and an otherend opened in a compressed gas flow path in the blast nozzle 8 or at anejection port of the blast nozzle 8, the liquid introduction path 88being configured to cause a liquid introduced from the liquid supplysource to strike with a stream of compressed gas flowing through theblast nozzle 8 or a stream of compressed gas ejected from the blastnozzle 8 to atomize the liquid, and

a flow rate control means such as a flow control valve 7 or a pumpprovided between the liquid introduction path 88 and the liquid supplysource.

In the blasting apparatus 1 configured as described above, the blastnozzle 8 is a suction-type blast nozzle having a nozzle tip 82 directedin the ejection direction of a rear nozzle 83 communicated with acompressed gas supply source (not shown), and an abrasive introductionchamber 85 communicated with an abrasive supply source between the rearnozzle 83 and the nozzle, the blast nozzle 8 being configured to createa negative pressure in the abrasive introduction chamber 85 by ejectionof a stream of compressed gas from the rear nozzle 83 to suck anabrasive in the abrasive supply source, and eject the compressed gas andthe abrasive as a mixed fluid, and

the other end (distal end 88 a) of the liquid introduction path 88 isopened in a compressed gas flow path 86 formed in the rear nozzle 83 orin front of an ejection port of the rear nozzle 83.

In the blasting apparatus 1 configured as above, the liquid introductionpath 88 may be formed by a conduit inserted concentrically in thecompressed gas flow path 86 provided in the rear nozzle 83, and theother end (distal end 88 a) of the liquid introduction path 88 may beopened at the ejection port of the rear nozzle 83.

The blasting apparatus 1 may further comprise a fixed quantity liquidsupply means such as a pump for supplying the liquid in the liquidsupply source to the liquid introduction path 88 in a fixed quantity.

Effect of the Invention

According to the blasting method and blasting apparatus of the presentinvention having the configuration of the present invention as describedabove, the following remarkable effects can be obtained.

Because a liquid such as water is atomized by causing it to strike withthe compressed gas flowing through the blast nozzle 8 or the compressedgas ejected from the blast nozzle 8, and because the amount of liquidthat is introduced into the blast nozzle is limited to 0.06 to 150cc/min, the atomized liquid is quickly evaporated into water vapor inthe space between the blast nozzle 8 and the workpiece W or on thesurface of the workpiece W because of the pressure drop after theejection from the blast nozzle 8 and the heat that is produced when theabrasive strikes with the workpiece W. This increases the humidity inthe processing chamber 21 to prevent the generation of staticelectricity.

In addition, the blasting method of the present invention, which doesnot wet the workpiece W or even if the method wets the workplace W,however, wet degrees are small compared to known wet blasting in spiteof the prevention of the generation of static electricity as describedabove, is applicable to a workpiece made of a material that should avoidcontact with water by adjusting the water supply conditions, and doesnot require additional steps such as washing and drying after theprocessing.

Further, in addition to the effect of preventing the generation ofstatic electricity as described above, the blasting method of thepresent invention has new unexpected effects including the improvementof the processing amount (cutting speed or rate) that is greater thanthat obtainable by a known dry blasting method, prevention of stickingor lodging of the abrasive into the surface of the workpiece, reductionof consumption of the abrasive, improvement of cutting speed or rate andefficiency of removal of a coated film and burrs, reduction ofelongation and warpage of the workpiece, and prevention of temperaturerise of the workpiece and the resulting reduction of burning of theproduct.

Although the reason for the effects, such as the increase in the cuttingspeed or rate, is not known, it seems probable that the effects resultfrom the fact that the liquid which is sprayed in an atomized state as aresult of the strike with a stream of compressed gas and turns intomicrodroplets because of the rapid decrease in pressure after theejection from the blast nozzle, evaporates quickly in the space in frontof the workpiece or on the surface of the workpiece upon contact withthe workpiece heated by the strike with the abrasive, and absorbs alarge amount of vaporization heat from the surrounding air and thesurface of the workpiece during evaporation (spray cooling).

When consideration is given to the improvement in the processing amount(cutting speed or rate) among the effects described above as oneexample, it is concluded that one possible reason for the smallerprocessing amount (cutting speed or rate) in wet blasting than in dryblasting is that the water ejected together with the abrasive forms awater film on the surface of the workpiece and the water film absorbsthe strike energy of the abrasive just about being struck with thesurface of the workpiece.

However, in the method of the present invention, because the liquidejected in an atomize state evaporates immediately after exiting theblast nozzle 8 as described above, the workpiece W does not get wet oreven if it gets wet, however, wet degrees are small compared to knownwet blasting. It is therefore believed that the strike energy can bemaintained at the same level as in dry blasting, and, consequently, alarge processing amount can be maintained even when a liquid is ejected.

On the other hand, one reason for the lower cutting speed or rate in dryblasting is believed to be that the surface temperature of the workpieceincreases as a result of the strike with the abrasive and thetemperature rise makes the surface of the workpiece soft enough toabsorb the strike energy of the abrasive.

In contrast to this, in the method of the present invention, the spraycooling as described above prevents the increase in surface temperatureof the workpiece and enables the processing to be carried out with thesurface hardness of the workpiece maintained. This is believed to be thereason why the processing amount (cutting speed or rate) is improvedcompared even to dry blasting.

The blasting method of the present invention described above can beachieved by making relatively simple structural changes in theconfiguration of an existing dry blasting apparatus, i.e., by replacingthe blast nozzle with a blast nozzle 8 that can eject a liquid asdescribed above, and adding a liquid supply source for supplying theliquid to the blast nozzle 8 and a flow rate control means such as aflow control valve 7 or a pump for controlling the amount of the liquidto be supplied to the blast nozzle 8.

In the configuration in which a conduit is concentrically inserted asthe liquid introduction path 88 in the compressed gas flow path 86 ofthe rear nozzle 83 of the blast nozzle 8 with an other end (distal end88 a) opened at the ejection port of the rear nozzle 83, the negativepressure resulting from the ejection of the compressed gas from the rearnozzle 83 can be used to introduce the liquid through the liquidintroduction path 88, and there is no need to provide an additionalmeans for supplying the liquid such as a pump, furthermore, theintroduction of the liquid is started and stopped in synchronizationwith the start and stop of the introduction of the compressed gas intothe blast nozzle 8. Consequently, there is no need to provide anadditional means for starting and stopping the supply of the liquid.Further, existing facilities can be used as long as the rear nozzle 83of the blast nozzle 8 is replaced.

However, a fixed quantity supply means such as a pump for supplying afixed quantity of liquid from the liquid supply source to the liquidintroduction path 88 may be provided. In this case, the design latitudefor the position at which the liquid is introduced into the blast nozzle8 increases and the liquid can be supplied more stably and reliably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram illustrating one configuration exampleof a blasting apparatus of the present invention;

FIGS. 2A and 2B are explanatory diagrams of a blast nozzle provided inthe blasting apparatus of the present invention. FIG. 2A is across-sectional view of the entire blast nozzle and FIG. 2B is anexplanatory diagram illustrating modifications of a nozzle tip;

FIGS. 3A and 3B are explanatory diagrams of the position at which aliquid is introduced into the blast nozzle (suction-type). FIG. 3A is anexplanatory diagram of the position at which a liquid is introduced intoa blast nozzle having an ordinary nozzle tip and FIG. 3B is anexplanatory diagram of the position at which a liquid is introduced intoa blast nozzle having a divided-continuous nozzle tips (822, 821);

FIGS. 4A and 4B are explanatory diagrams of the position at which aliquid is introduced into the blast nozzle (direct-pressure type). FIG.4A is an explanatory diagram of the position at which a liquid isintroduced into a blast nozzle having an ordinary nozzle tip and FIG. 4Bis an explanatory diagram of the position at which a liquid isintroduced into a blast nozzle having a divided-continuous nozzle tips(822′, 821′);

FIG. 5 is a cross-sectional view of another blast nozzle provided in theblasting apparatus of the present invention;

FIG. 6 is a graph showing the changes in processing amount with changesin water supply amount (boron plate);

FIG. 7 is a graph showing the changes in processing amount with changesin water supply amount (carbide plate);

FIG. 8 is a graph showing the changes in processing amount with changesin water supply amount (urethane rubber plate);

FIG. 9 is a graph showing the changes in processing amount with changesin water supply amount (aluminum plate);

FIG. 10 is a graph showing the changes in processing amount with changesin water supply amount (stainless plate);

FIG. 11 is a graph showing the changes in processing amount with changesin water supply amount (iron plate);

FIG. 12 is a graph showing the changes in processing amount with changesin water supply amount (acrylic plate);

FIG. 13 is a graph showing the changes in processing amount with changesin water supply amount (epoxy glass plate);

FIG. 14 is a graph showing the changes in processing amount with changesin water supply amount (granite);

FIG. 15 is a graph showing the changes in the amount of abrasive stuckwith changes in water supply amount (urethane rubber);

FIG. 16 is a graph showing the changes in the amount of abrasive stuckwith changes in water supply amount (stainless);

FIG. 17 is a graph showing the changes in the amount of abrasive stuckwith changes in water supply amount (iron);

FIG. 18 is a graph showing the changes in the amount of abrasive stuckwith changes in water supply amount (acrylic);

FIG. 19 is a graph showing the changes in the amount of abrasive stuckwith changes in water supply amount (epoxy glass);

FIG. 20 shows photographs showing the particle structures of an abrasiveafter use in a blasting method of the present invention (example) and anabrasive used in a dry blasting method (comparative example);

FIGS. 21A and 21B show surface roughness data of polycarbonate productsafter stripping paint by blasting. FIG. 21A shows the data of a producttreated by a method of the present invention (example) and FIG. 21Bshows the data of a product treated by dry blasting (comparativeexample);

FIGS. 22A and 22B show surface roughness data of polyphenylene sulfideproducts after deburring by blasting. FIG. 22A shows the data of aproduct treated by a method of the present invention (example) and FIG.22B shows the data of a product treated by dry blasting (comparativeexample);

FIG. 23 is a correlation diagram showing the changes in time until thecoverage reaches 100% with changes in nozzle distance; and

FIG. 24 is a correlation diagram showing the changes in time until thecoverage reaches 100% with changes in particle size of the abrasive.

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is next described below withreference to the accompanying drawings.

1. Blasting Apparatus (1) General Configuration

One configuration example of a blasting apparatus 1 of the presentinvention is shown in FIG. 1.

As shown in FIG. 1, the blasting apparatus 1 includes a compressed gassupply source (not shown), an abrasive tank 3 as an abrasive supplysource, and a blast nozzle 8 for merging a compressed gas introducedfrom the compressed gas supply source with an abrasive from the abrasivetank 3 and ejecting the mixture. In the illustrated embodiment, theblasting apparatus 1 is constituted as what is called a “suction-type”blasting apparatus in which the abrasive from the abrasive tank 3 whichis sucked by a negative pressure created in the blast nozzle 8 by theintroduction of the compressed gas from the compressed gas supplysource, is merged with a stream of the compressed gas and ejected onto aworkpiece W. In this embodiment, the gas is compressed air.

In the illustrated embodiment, the blasting apparatus 1 includes aprocessing chamber 21 formed in a cabinet 2 accommodating the blastnozzle 8, the abrasive tank 3 which is a cyclone communicated with ahopper formed at a lower end of the processing chamber 21 via anabrasive recovery pipe 91, and a dust collector 5 for sucking the insideof the abrasive tank 3. When the abrasive is ejected from the blastnozzle 8 accommodated in the processing chamber 21 with an exhauster 6in the dust collector 5 being actuated to suck the inside of theabrasive tank 3 as a cyclone, the ejected abrasive is introduced intothe abrasive tank 3 through the abrasive recovery pipe 91 together withswarf and other objects. As a result of air classification in theabrasive tank 3, reusable abrasive is recovered to the bottom of theabrasive tank 3 and crushed abrasive and dust are sucked and removed bythe dust collector 5. The recovered abrasive can be cyclically used.

The basic configuration of the blasting apparatus 1 is not limited tothe circulation type configuration in which the abrasive is cyclicallyused as described above. For example, the blasting apparatus 1 may havea batch-type configuration in which the abrasive after use is not reusedbut is disposed of after each use. In this case, the configurationprovided for air classification of the dust including swarf and theabrasive may be omitted and the dust collector 5 may be used to removeor collect the abrasive after use and dust in the processing chamber 21together.

While the description is made based on the assumption that the blastingapparatus is constituted as a suction-type in the illustrated example,the present invention is also applicable to a direct-pressure typeblasting apparatus in which a compressed gas in a pressurized tank andan abrasive are introduced together into a blast nozzle and ejectedtherefrom, for example. Any of various structures employed in knownblasting apparatuses can be employed as a basic configuration of theblasting apparatus.

In the blasting apparatus 1 of the present invention, a liquid, in thisembodiment, water, is introduced into the blast nozzle 8. The water iscaused to strike with a stream of compressed gas flowing through theblast nozzle 8 to atomize it into droplets with an average particlediameter of 1 mm or less, preferably 300 μm or less, more preferably 100μm or less, and the atomized liquid is incorporated into the compressedgas immediately before it is ejected onto the workpiece W. In this way,the atomized liquid can be sprayed onto the workpiece W together withthe abrasive.

In order to make it possible to incorporate the atomized liquid into thecompressed gas ejected toward the workpiece W as described above, theblasting apparatus 1 of the present invention is provided with a liquidsupply source (not shown) for supplying a liquid (water) to the blastnozzle 8, and has a liquid introduction path 88 in the blast nozzle 8through which the water supplied from the liquid supply source isintroduced into the blast nozzle 8, and a flow rate control meansconstituted of a flow control valve 7 or a pump in a conduitcommunicating the liquid supply source and the liquid introduction path88 of the blast nozzle 8.

(2) Blast Nozzle

An example of a configuration of the blast nozzle 8 provided in theblasting apparatus 1 of the present invention is shown in FIG. 2.

The blast nozzle 8 shown in FIG. 2 has the basic structure of anexisting suction-type blast nozzle, and is constituted of a body 81forming a primary part of the blast nozzle 8, and a nozzle tip 82 and arear nozzle 83 attached to the body 81.

The body 81 is provided with an abrasive introduction port 84 throughwhich the abrasive supplied from the abrasive tank 3 as an abrasivesupply source is introduced, and an abrasive introduction chamber 85formed therein in communication with the abrasive introduction port 84and having the shape of a generally cylindrical container.

The nozzle tip 82 attached to the body 81 has a conical inner surface 82a tapered conically, and is configured such that the abrasiveintroduction chamber 85 formed in the body 81 and a flow path in thenozzle tip having the conical inner surface 82 a are communicated witheach other when the nozzle tip 82 is attached to a front end side of thebody 81.

As shown in FIG. 2B, the nozzle tip 82 may be either one having acircular opening (round type) or one having a slit-like opening (slittype), and the flow path formed therein may have a venturi-type shapewith a cross-section that first narrows from its entrance and thenwidens again toward the exit.

The rear nozzle 83 is attached to a rear end side of the body 81 withits distal end pointing toward the center of the conical inner surface82 a of the nozzle tip 82. The blast nozzle 8 is the same inconfiguration as a known suction-type blast nozzle 8 in that when thecompressed gas from the compressed gas supply source (not shown) isejected from the rear nozzle 83, the abrasive from the abrasive tank 3,which is sucked into the abrasive introduction chamber 85 by a negativepressure created by the ejection of the compressed gas from the rearnozzle 83, is merged into the compressed gas ejected from the rearnozzle 83 and ejected from the distal end of the nozzle tip 82.

The blast nozzle 8 for use in the blasting apparatus 1 of the presentinvention is provided with a liquid introduction path 88 through whichthe liquid from the liquid supply source (not shown) is introduced intothe blast nozzle 8 so that the liquid can be atomized and sprayed asdescribed above. The liquid introduction path 88 has a distal end 88 aopening in a compressed gas flow path formed in the blast nozzle 8, forexample, in a compressed gas flow path 86 formed in the rear nozzle 83,in front of the delivery port of the rear nozzle 83, in the flow path inthe nozzle tip 82, or at the ejection port of the blast nozzle 8, sothat the liquid can be atomized by causing it to strike with ahigh-speed stream of compressed gas flowing through the blast nozzle 8or a high-speed stream of compressed gas ejected from the blast nozzle 8and sprayed.

In the present invention, a mesh material may be provided in the openingat the distal end 88 a of the liquid introduction path 88 so that theliquid can be atomized in a more preferred manner when the liquidejected from the distal end 88 a of the liquid introduction path 88 isatomized by causing it to strike with a high-speed stream of compressedgas. In this case, the liquid is atomized in a more preferred mannerbecause the liquid supplied through the liquid introduction path 88 ispreliminarily atomized through the mesh material before it is caused tostrike with the high-speed stream of compressed gas.

The mesh material for use in the present invention is not particularlylimited. For example, various types of mesh materials, such as oneobtained by weaving wires made of a metal or a resin into a flat mesh orone formed by creating fine pores through a plate, can be used.

In the embodiment shown in FIG. 2, the conduit as the liquidintroduction path 88 is arranged concentrically in the compressed gasflow path 86 formed through the rear nozzle 83 so that the compressedgas can flow between the interior wall of the compressed gas flow path86 and the exterior wall of the liquid introduction path 88, and thedistal end 88 a of the liquid introduction path 88 is opened at the sameposition as the opening of the rear nozzle 83 in order to cause theliquid ejected from the distal end 88 a of the liquid introduction path88 to strike with the high-speed high-pressure stream of compressed gasflowing along the outer periphery of the liquid to atomize it.

In the blasting apparatus 1 of this embodiment constituted as describedabove, because the liquid is sucked out of the distal end 88 a of theliquid introduction path 88 by the effect of a negative pressure createdin the abrasive introduction chamber 85 and merged with the stream ofcompressed gas, the liquid can be atomized in the blast nozzle 8 withouta fixed quantity liquid supply device such as a pump for supplying theliquid from a liquid supply source (not shown) such as a liquid tankinto the blast nozzle 8. In addition, because the introduction of theliquid from the liquid supply source automatically starts and stops insynchronization with the start and stop of the introduction of thecompressed gas into the blast nozzle 8, dripping and other troublescaused by failure to start or stop the supply of the liquid does notoccur.

The configuration for causing the liquid to strike with the stream ofcompressed gas is not limited to the configuration shown in FIG. 2, andthe configuration of any of various known gas-blast type two-fluidnozzles (atomizers) may be applied to that of the rear nozzle 83. Asdescribed above, the introduction of the liquid into the blast nozzlemay be achieved by fixed quantity liquid introduction means, such as apump, provided in the tank as a liquid supply source or in the pipebetween the liquid supply source and the blast nozzle instead of theconfiguration that uses a negative pressure in the abrasive introductionchamber.

The position at which the liquid is supplied into the blast nozzle 8 maybe different from the position shown in FIG. 2. For example, the liquidmay be introduced into the suction-type blast nozzle through a spaceformed around the outer periphery of a distal portion of the rear nozzle83 of the blast nozzle 8 as the liquid introduction path 88 and openingtoward the distal end of the rear nozzle 83 as shown in FIG. 5. When theliquid is introduced into the liquid introduction path 88, it is ejectedto surround the outer periphery of the compressed gas ejected from therear nozzle 83 and atomized upon strike with the high-speed,high-pressure stream of compressed gas.

Further, as shown in FIG. 3A, the distal end 88 a of the liquidintroduction path 88 may be opened in the abrasive introduction chamber85 or at the position where the ejection port of the blast nozzle 8 isformed so that the liquid in the liquid introduction path 88 can besucked out by a negative pressure created by the stream of compressedgas and caused to strike with the stream of compressed gas flowingthrough the blast nozzle 8 or the stream of compressed gas ejected fromthe blast nozzle 8. Alternatively, the liquid in the liquid supplysource may be supplied in a fixed quantity by a pump into a compressedgas flow path formed through the rear nozzle 83 or into a compressed gasflow path formed through the nozzle tip 82. In place of or in additionto introducing the liquid at the position described with reference toFIG. 2A or FIG. 5, the liquid may be introduced at one or more of thepositions shown in FIG. 3A.

The nozzle tip 82 may be constituted to have two divided nozzle tips 821and 822 coaxially and sequentially arranged in a longitudinal directionas shown in FIG. 3B so that, when a fluid is introduced from the nozzletip 821 having a small-diameter flow path formed therethrough into thenozzle tip 822 having a large-diameter flow path formed therethrough,air is sucked in through a vent 823 formed at the interface between thenozzle tips 821 and 822 and ejected after merged water with the streamof abrasive. When a liquid is introduced into the nozzle tip 82 havingsuch a structure, the liquid may be introduced through the vent 823 ofthe nozzle tip 82.

In a direct-pressure type blast nozzle, the distal end 88 a of theliquid introduction path 88 may be opened at the position where theejection port of the blast nozzle 8 is formed as shown in FIG. 4A sothat the liquid in the liquid introduction path 88 is sucked out by theeffect of a negative pressure created by the ejection of the compressedgas and caused to strike with the compressed gas ejected from the blastnozzle 8. Alternatively, the distal end 88 a of the liquid introductionpath 88 may be opened in a compressed gas flow path in a rear nozzle 83′provided in a blast nozzle body 81′ or in a compressed gas flow pathformed through a nozzle tip 82′ attached to the distal end of the blastnozzle 8, and the liquid from the liquid supply source may be introducedinto the blast nozzle 8 by a pump. The liquid can be introduced at anyone or more of these positions.

A divided-continuous nozzle tip having two longitudinally-divided nozzletips 821′ and 822′ arranged coaxially and sequentially in a longitudinaldirection as shown in FIG. 4B can be also used as a nozzle tip 82′ inthe configuration of the above direct-pressure type blast nozzle. Inthis case again, the liquid may be introduced through a vent 823′provided at the interface between the two nozzle tips 821′ and 822′.

A flow rate control means for controlling the flow rate of liquid thatis introduced into the liquid introduction path 88 is provided in theconduit extending from the liquid supply source to the liquidintroduction path 88 so that the amount of liquid that is introducedinto the blast nozzle 8 can be adjusted.

In this embodiment, a flow control valve 7 is provided as the flow ratecontrol means in the conduit between the liquid introduction path 88having the distal end 88 a opened at a position where a negativepressure is created and the liquid supply source. While a valve whoseopening is adjustable at eight levels is used as the flow control valve7 in this embodiment, a valve whose opening is continuously adjustablemay be used. Any type of valve may be used as long as the flow rate ofliquid can be adjusted.

A pump is provided as the flow rate control means between the liquidintroduction path 88 having the distal end 88 a opened at a positionother than the position where a negative pressure is created and theliquid supply source so that the amount of liquid that is supplied intothe blast nozzle 8 can be controlled by controlling the operating speedof the pump, such as the rotational speed of the motor for driving thepump.

A pump may be provided between the liquid introduction path 88 and theliquid supply source as shown as modifications in FIG. 3A and FIG. 4Aeven when the distal end 88 a of the liquid introduction path 88 isopened at the position where a negative pressure is created, and a flowcontrol valve may be provided on the secondary side of the pump so thatthe flow rate of liquid that is introduced into the blast nozzle 8 canbe adjusted even when a pump is provided.

Further, the liquid introduction path 88 may be connected to a waterintake (faucet) of the water supply system so as to use the water supplysystem as a liquid supply source, without providing a container such asa liquid tank as a liquid supply source. In this case, the feed-waterpressure from the water supply system may be used to introduce theliquid into the liquid introduction path 88 and omit the installation ofthe pump.

2. Effects

Taking the case as an example where the blasting apparatus 1 in FIG. 1constituted as described above is equipped with the blast nozzle 8 shownin FIGS. 2A and 2B, the explanation of its operation is given below.

An abrasive is placed in the abrasive tank 3 as an abrasive supplysource, and the liquid tank (not shown) as a liquid supply source isfilled with a liquid such as water. In this state, the introduction of acompressed gas into the blast nozzle 8 from the compressed gas supplysource (not shown) is started.

When the introduction of the compressed gas is started in this way, ahigh-speed compressed gas is ejected from the distal end of the rearnozzle 83 of the blast nozzle 8. Then, in the nozzle tip 82, ahigh-speed gas stream toward its ejection port is generated.

Thus, the gas in the abrasive introduction chamber 85 is drawn into thenozzle tip 82 by the stream of compressed gas. As a result, a negativepressure is created in the abrasive introduction chamber 85, and theabrasive from the abrasive tank 3 is introduced into the abrasiveintroduction chamber 85 through the abrasive introduction port 84. Atthe same time, the liquid in the liquid introduction path 88 is suckedout of the distal end 88 a of the liquid introduction path 88 by thenegative pressure. The sucked-out liquid is atomized by the high-speedcompressed gas ejected from the rear nozzle 83 and incorporated into thecompressed gas together with the abrasive before it is sprayed from theblast nozzle 8.

In the blasting method of the present invention, a preferred ejectionamount of the abrasive is 2 g/min to 20 kg/min, whereas the amount ofliquid that is introduced into the blast nozzle 8 is as relatively smallas 0.06 cc/min to 150 cc/min. In addition, the liquid ejected togetherwith the abrasive is atomized upon strike with the high-speed compressedgas flowing through the blast nozzle 8 before being sprayed from theblast nozzle 8. Further, because the compressed gas ejected from theblast nozzle 8 undergoes a rapid decrease in pressure and because thesurface of the workpiece is heated by the strike with the abrasive, thesprayed liquid evaporates in the space between the blast nozzle 8 andthe workpiece W or on the surface of the workpiece W and absorbs a largeamount of vaporization heat from the space and the surface of theworkpiece W.

As a result, it is believed that, when blasting is carried out by themethod of the present invention, not only the generation of staticelectricity is prevented by the increase in humidity resulting from theevaporation of the liquid but also several other benefits, including theimprovement of the cutting speed or rate, improvement of the efficiencyof removal of a coated film or burrs, prevention of sticking or lodgingof the abrasive into the surface of the workpiece W, and prevention ofwarpage or elongation of the workpiece, can be obtained in contrast toordinary blasting that does not involve spraying of a liquid.

In other words, in the method of the present invention, water is ejectedbut the ejected water evaporates quickly as described above. Thus, thesurface of the workpiece does not get wet or even if it gets wet,however, wet degrees are small compared to known wet blasting, and theformation of a water film that absorbs the strike energy of the abrasiveon the surface of the workpiece is prevented.

On the other hand, although the above-mentioned formation of a waterfilm is prevented, because the sprayed water absorbs a large amount ofvaporization heat when it evaporates, the surface temperature of theworkpiece is prevented from increasing. As a result, the absorption ofthe strike energy from the abrasive due to softening of the surface ofthe workpiece, a coated film formed on the surface of the workpiece orburrs as the object of removal can be prevented. This is believed to bethe reason why the processing amount is improved and the efficiency ofremoval of a coated film or burrs is improved compared to dry blastingin which such softening can occur.

It is believed that the sticking or lodging of abrasive as describedabove also occurs because the ejected abrasive sticks into the surfaceof the workpiece more easily as the surface of the workpiece becomessofter with increase in temperature.

In addition, it is believed that elongation and warpage that reduce thedimensional stability of the product occurs because of elongation of theworkpiece due to temperature rise and a difference in elongation betweenthe front and back sides of the workpiece, respectively.

It is, therefore, believed that the above effects can be obtained whenblasting is carried out by the method of the present invention becausethe workpiece is protected from wetting and temperature rise.

It has been also observed that the abrasive recovered in the blastingmethod of the present invention has undergone less cracking and chippingthan that of conventional blasting carried out without spraying a liquidalthough its principle is unknown. This means that the blasting methodof the present invention can reduce the rate of consumption of theabrasive.

As described above, the blasting method of the present invention caneffectively prevent the generation of sparks caused by accumulation ofstatic electricity during processing and can therefore eliminate notonly breakage or failure of the products themselves, in particular,items such as electronic components but also breakage of electrodes andother parts provided on the product.

In addition, not only the products are prevented from accumulation ofstatic electricity but also the abrasive and the abrasive circulatingsystem including the interior walls of the cabinet and the interiorwalls of the ducts are prevented from accumulation of staticelectricity. Several other benefits can be achieved including theprevention of the abrasive from adhering to the interior of the cabinet2 and the abrasive tank 3, and improvement of abrasive recoveryefficiency resulting from a decrease in the amount of abrasive that isnot recovered but flows to a dust collector, because the abrasive in aswirling flow strikes with the abrasive adhering to the interior of thecyclone-type abrasive tank 3.

In addition, the blasting method of the present invention has beneficialeffects that cannot be predicted from conventional arts including theimprovement of processing amount as compared to ordinary dry blasting,improvement of the efficiency of removal of a coated film or burrs,reduction of surface roughness, prevention of change in color due toburning, prevention of sticking or lodging of abrasive that may causecontamination during subsequent painting or plating, and prevention ofwarpage and elongation of the workpiece that reduces the dimensionalstability of the product in addition to the effect of preventing thegeneration of static electricity.

Examples

The results of tests conducted to confirm that the blasting method ofthe present invention can provide the above-mentioned benefits are shownbelow.

The dry blasting (comparative example) and the blasting of the presentinvention (examples) were both carried out using a suction-type blastingapparatus (see FIG. 1 for the outline of the structure) as the blastingapparatus. In the blasting of the present invention (example), whichinvolves the supply of a liquid (water), either the blast nozzle havingthe liquid introduction path 88 in the compressed gas flow path 86 ofthe rear nozzle 83 as described with reference to FIG. 2A or the blastnozzle 8 having a chamber as the liquid introduction path 88 around adistal portion of the rear nozzle 83 as described with reference to FIG.5 was used. On the other hand, the dry blasting (comparative example)was carried out by ejecting an abrasive from the blast nozzle 8 shown inFIG. 2A or FIG. 5 without supplying water to conduct measurement, orusing a blast nozzle 8 equipped with an ordinary rear nozzle (having astructure obtained by removing the liquid introduction path 88 from therear nozzle 83 of the blast nozzle 8 having a structure shown in FIG.2(A)) to conduct measurement.

(1) Confirmation of Antistatic Effect

Blasting was performed on an acrylic plate (100 mm×100 mm×5 mm) and theaccumulated amount of static electricity was measured.

Nylon beads (NB) #0303 (average particle diameter: 300 μm) manufacturedby Fuji Manufacturing Co., Ltd. were used as the abrasives, and theabrasives were ejected at a nozzle distance of 160 mm and an ejectionpressure of 0.3 MPa for 40 minutes.

The processing was carried out using a circulating-type blastingapparatus having a structure shown in FIG. 1 and equipped with the blastnozzle 8 described with reference to FIG. 2A. The flow control valve 7for adjusting the amount of water introduced into the blast nozzle 8 wasgradually opened from its full-closed position to increase the watersupply amount. The changes in the accumulated amount of staticelectricity in the acrylic plate (measuring instrument: 709 STATICSENSOR manufactured by 3M was used) and the changes in temperature andhumidity in the processing chamber were measured and the condition inthe processing chamber was observed. The results of measurements areshown in Table 1.

TABLE 1 Result of test for static electricity accumulation AccumulatedTemperature Water amount of in the Ejected supply static processingamount amount electricity chamber of abrasive (cc/min) (kV) (humidity)550 g/min 0 −23.4 21.4° C. (24%) 0.06 −14.0 21.3° C. (24%) 0.15 −6.421.2° C. (25%) 0.50 −5.6 21.3° C. (24%) 1.0 −5.8 22.4° C. (23%) 2.0 −8.021.5° C. (24%) 3.0 −9.3 18.7° C. (25%) 4.0 −7.6 19.1° C. (24%) 5.0 −6.219.3° C. (24%) 6.0 −7.4 20.6° C. (24%) 7.0 −3.9 20.4° C. (24%) 8.1 −5.019.7° C. (24%) 1150 g/min 8.0 −9.9 20.1° C. (25%) 9.1 −7.4 21.6° C.(25%) 10.0 −5.2 21.5° C. (25%) 11.0 −5.2 21.2° C. (24%) 12.2 −6.4 21.2°C. (24%) 13.1 −5.6 20.8° C. (25%) 14.1 −4.0 20.8° C. (25%) 15.0 −2.021.3° C. (25%) 16.2 −2.1 21.1° C. (25%) 17.1 −2.2 21.2° C. (25%)

It was confirmed from the above results that the accumulated amount ofstatic electricity was decreased by 40% or more simply by supplying assmall an amount of water as 0.06 cc/min compared to the value obtainedwhen dry blasting was carried out without supplying water with the flowcontrol valve 7 fully closed. It was therefore confirmed that sprayingeven a relatively small amount of water was highly effective inpreventing the generation of static electricity.

After that, the accumulated amount of static electricity furtherdecreased as the water supply amount was increased. The accumulatedamount of static electricity decreased by 90% or more at 15.0 cc/mincompared to the value obtained when no water was supplied.

The abrasive had adhered everywhere in the cabinet including the surfaceof the workpiece, the interior walls of the cabinet, rubber hoses andthe surface of the blast nozzle after blasting was carried out withoutsupplying water with the flow control valve 7 fully closed, whereasadhesion of abrasive due to static electricity was not observed afterblasting was carried out by the method of the present invention althoughaccumulation of abrasive was observed on uneven parts of the walls inthe cabinet.

(2) Confirmation of Increase in Processing Amount (Cutting Speed orRate)

(2-1) Measurement of Changes in Processing Amount with Changes in WaterSupply Amount

The blast nozzle shown in FIG. 2A was used, and the opening of the flowcontrol valve was adjusted to measure how the processing amount (cutamount) for the workpiece changed with changes in the water supplyamount to the blast nozzle.

Test pieces made of the materials shown in Table 2 below were processedusing an alumina abrasive (“FUJIRUNDUM A#60” manufactured by FujiManufacturing Co., Ltd.) at an ejection distance of 120 mm and anejection pressure of 0.4 MPa under conditions shown again in Table 2.The weights of the test pieces before and after the processing weremeasured, and the decrease in weight was taken as the cut amount.

TABLE 2 Test pieces and measurement method Amount of abrasive Dimensionsused Processing Test pieces (mm) (kg) time Boron plate (B4C) 106 × 60 ×5.5 6 60 (min) Carbide plate (D-40)  60 × 45 × 7 3 30 (min) Urethanerubber (TR100-70°)  80 × 80 × 10 3 60 (min) Aluminum plate  80 × 80 × 103 30 (min) Stainless plate (SUS304) 100 × 100 × 6 3 30 (min) Iron plate(SS41) 100 × 100 × 6 3 30 (min) Acrylic plate (thermoplastic)  80 × 80 ×5 3 90 (sec) Epoxy glass plate (thermosetting)  80 × 80 × 5 3 90 (sec)Granite  80 × 80 × 10 3 30 (sec)

The results of measurement on each test piece are shown in Tables 3 to11 and FIGS. 6 to 14. The ratio of decrease in Tables 3 to 11 is theratio of the decrease in weight to the decrease in weight obtained whenprocessing was carried out without supplying water.

TABLE 3 Changes in processing amount with changes in water supply amount(boron plate) Water Weight of test piece (g) supply Decrease in amountBefore After weight (ratio (cc/min) processing processing of decrease)Comparative 0 79.59 78.54 −1.05 (1) example Example 0.1 82.15 81.00−1.15 (1.1) 0.5 78.97 77.45 −1.52 (1.45) 2.0 81.56 78.86 −2.70 (2.57)3.0 83.56 80.50 −3.06 (2.91) 5.0 83.37 80.33 −3.04 (2.89) 7.0 83.9180.86 −3.05 (2.90) 10.0 83.50 80.41 −3.09 (2.94) 13.0 79.14 76.14 −3.00(2.86) 18.0 78.85 75.84 −3.01 (2.87) 24.0 83.54 80.56 −2.98 (2.84)

TABLE 4 Changes in processing amount with changes in water supply amount(carbide plate) Water Weight of test piece (g) supply Decrease in amountBefore After weight (ratio (cc/min) processing processing of decrease)Comparative 0 254.84 244.94  −9.90 (1) example Example 1.0 273.13 262.53−10.60 (1.07) 3.0 265.34 254.24 −11.10 (1.12) 5.0 273.24 261.86 −11.35(1.15) 12.0 262.53 250.93 −11.60 (1.17) 20.0 260.30 248.16 −12.14 (1.22)28.0 206.02 193.45 −12.57 (1.27)

TABLE 5 Changes in processing amount with changes in water supply amount(urethane rubber plate) Water Weight of test piece (g) supply Decreasein amount Before After weight (ratio (cc/min) processing processing ofdecrease) Comparative 0 74.61 74.50 −0.11 (1) example Example 3.0 74.7874.58 −0.20 (1.82) 8.0 74.75 73.76 −0.99 (9.00) 16.0 74.81 72.73 −2.08(18.91) 28.0 75.19 72.31 −2.88 (26.18) 40.0 74.57 71.31 −3.26 (29.64)50.0 75.13 71.96 −3.17 (28.82) 60.0 74.43 71.25 −3.18 (28.91)

TABLE 6 Changes in processing amount with changes in water supply amount(aluminum plate) Water supply Weight of test piece (g) amount BeforeAfter Decrease in weight (cc/min) processing processing (ratio ofdecrease) Comparative 0 166.36 163.93 −2.43 (1)   example Example 3.0164.98 160.40 −4.58 (1.88) 8.0 165.24 160.09 −5.15 (2.12) 16.0 165.22159.90 −5.32 (2.19) 32.0 165.00 159.40 −5.60 (2.30) 50.0 164.71 158.98−5.73 (2.36) 70.0 165.89 160.05 −5.84 (2.40) 100.0 166.17 160.50 −5.67(2.33) 130.0 166.04 160.39 −5.65 (2.33) 150.0 167.67 162.11 −5.56 (2.29)

TABLE 7 Changes in processing amount with changes in water supply amount(stainless plate) Water supply Weight of test piece (g) amount BeforeAfter Decrease in weight (cc/min) processing processing (ratio ofdecrease) Comparative 0 450.59 445.18 −5.41 (1)   example Example 1.0449.89 443.65 −6.24 (1.15) 3.0 450.99 443.46 −7.53 (1.39) 5.0 450.20442.45 −7.75 (1.43) 8.0 449.76 442.04 −7.72 (1.43) 12.0 450.94 443.18−7.76 (1.43) 20.0 450.88 442.99 −7.89 (1.46) 30.0 450.27 442.34 −7.93(1.47) 40.0 449.54 441.57 −7.97 (1.47) 50.0 450.66 442.76 −7.90 (1.46)60.0 450.23 442.22 −8.01 (1.48)

TABLE 8 Changes in processing amount with changes in water supply amount(iron plate) Water supply Weight of test piece (g) amount Before AfterDecrease in weight (cc/min) processing processing (ratio of decrease)Comparative 0 462.72 457.90 −4.82 (1)   example Example 1.0 462.86456.90 −5.96 (1.24) 3.0 462.20 455.02 −7.18 (1.49) 5.0 462.40 455.11−7.29 (1.51) 8.0 462.46 455.22 −7.24 (1.50) 12.0 462.94 455.55 −7.39(1.53) 20.0 462.20 454.65 −7.55 (1.57) 30.0 461.73 454.02 −7.71 (1.60)40.0 463.07 455.24 −7.83 (1.62) 50.0 462.63 454.50 −8.13 (1.69) 60.0462.38 454.13 −8.25 (1.71)

TABLE 9 Changes in processing amount with changes in water supply amount(acrylic plate) Water supply Weight of test piece (g) amount BeforeAfter Decrease in weight (cc/min) processing processing (ratio ofdecrease) Comparative 0 37.92 37.37 −0.55 (1)   example Example 1.037.90 37.19 −0.71 (1.29) 3.0 37.91 36.93 −0.98 (1.78) 6.0 37.92 36.72−1.20 (2.18) 10.0 37.91 36.55 −1.26 (2.29) 15.0 37.93 36.59 −1.34 (2.44)20.0 36.76 35.44 −1.32 (2.40) 30.0 36.66 35.34 −1.32 (2.40) 40.0 36.6735.32 −1.35 (2.45) 50.0 36.62 35.20 −1.42 (2.58) 60.0 36.56 35.11 −1.45(2.64)

TABLE 10 Changes in processing amount with changes in water supplyamount (epoxy glass plate) Water supply Weight of test piece (g) amountBefore After Decrease in weight (cc/min) processing processing (ratio ofdecrease) Comparative 0 61.90 60.04 −1.86 (1)   example Example 1.061.81 60.00 −1.81 (0.97) 3.0 61.83 59.38 −2.45 (1.32) 6.0 61.91 59.00−2.91 (1.56) 10.0 61.78 59.00 −3.06 (1.65) 15.0 61.83 58.64 −3.19 (1.72)20.0 61.77 58.58 −3.19 (1.72) 30.0 61.74 58.51 −3.23 (1.74) 40.0 61.8558.44 −3.41 (1.83) 50.0 61.92 58.49 −3.43 (1.84) 60.0 61.91 58.47 −3.44(1.85)

TABLE 11 Changes in processing amount with changes in water supplyamount (granite) Water supply Weight of test piece (g) amount BeforeAfter Decrease in weight (cc/min) processing processing (ratio ofdecrease) Comparative 0 185.22 182.34 −2.88 (1)   example Example 1.0180.55 177.12 −3.43 (1.19) 5.0 191.26 187.67 −3.59 (1.25) 10.0 187.87184.35 −3.52 (1.22) 25.0 187.06 183.47 −3.59 (1.25) 40.0 192.97 189.34−3.63 (1.26)

According to the above results, it was confirmed that the cut amountcould be increased compared to the value obtained when blasting wascarried out without supplying water (comparative example) regardless ofthe material of the test piece processed.

While the cut amount increased as the water supply amount was increased,the cut mount did not further increase but remained constant even if thewater supply amount was increased after the cut amount had increased toa certain level.

This indicates that ejecting a relatively small amount of liquidtogether with an abrasive as in the blasting method of the presentinvention has the unexpected effect of increasing the processing amountin addition to the above-mentioned antistatic effect.

In addition, it was confirmed that this effect could be obtainedregardless of the material of the workpiece.

(2-2) Confirmation of Effect of Different Abrasives on Processing Amount

The results of processing performed on stainless test pieces (SUS304) byejecting zircon grid (“FZG 60” manufactured by Fuji Manufacturing Co.,Ltd., particle diameter: 0.125 to 0.250 mm) using the blast nozzle shownin FIG. 5 and the results of processing performed on test pieces byejecting an alumina abrasive (“FUJIRUNDUM A #60” manufactured by FujiManufacturing Co., Ltd., average particle diameter: 230 μm) are shown inTables 12 and 13, respectively.

TABLE 12 Changes in processing amount depending on whether water issupplied (FZG-60) Comparative example Example Valve opening 0/8 (Fullclosed) 3/8 Water supply 0 3.0 amount (cc/min) Decrease in weight(1)−2.9 (1)−4.8 of test piece (2)−3.4 (2)−5.6 (g/20 min) (Average:−3.15) (Average: −5.2)

TABLE 13 Changes in processing amount depending on whether water issupplied (FUJIRUNDUM A #60) Comparative example Example Water supplyamount (cc/min) 0     2.0   3.6 Decrease in weight of test −11.52 −15.93−16.19 piece (g/1H)

It was confirmed from the above results that the processing amountincreased both when zircon grid (FZG-60) was used as the abrasive andwhen an alumina abrasive (“FUJIRUMDUM A #60” manufactured by FujiManufacturing Co., Ltd., particle diameter: 250 to 212 μm) was used. Itwas therefore confirmed that the processing amount increasing effect ofthe present invention could be still obtained even when the type ofabrasive used was different.

The increase in processing amount was more than 1.5 times for the zircongrid (FZG-60) and 1.3 to 1.4 times for the alumina abrasive (“FUJIRUNDUMA #60” manufactured by Fuji Manufacturing Co., Ltd.). It was thereforeconfirmed that a significant increase in processing amount could beachieved.

(3) Confirmation of Abrasive Sticking or Lodging State

The components at the center of the processed region of the urethanerubber plate, stainless plate, iron plate, acrylic plate and epoxy glassplate of the test pieces processed as described in “(2)(2-1) Measurementof changes in processing amount with changes in water supply amount”were measured with an EDX (energy dispersive X-ray analysis) device(INCA Energy manufactured by Oxford Instruments), and the massconcentration of aluminum as a primary component of the alumina abrasiveused (“FUJIRUNDUM A #60” manufactured by Fuji Manufacturing Co., Ltd.)was evaluated as the amount of abrasive stuck in the test piece.

The results of measurements are shown in Tables 14 to 18 and FIGS. 15 to19. The Al mass concentration ratio in Tables 14 to 18 is the ratio ofthe Al mass concentration to the Al mass concentration obtained withoutwater supply.

TABLE 14 Changes in amount of abrasive stuck in test piece with changesin water supply amount (urethane rubber) Water supply Al mass Al massamount (cc/min) concentration (%) concentration ratio Comparative 013.62 1 example Example 3.0 7.99 0.59 5.0 6.38 0.47 12.0 4.09 0.30 20.02.17 0.16 28.0 2.11 0.15 40.0 2.09 0.15 50.0 2.19 0.16 60.0 1.80 0.13

TABLE 15 Changes in amount of abrasive stuck in test piece with changesin water supply amount (stainless) Water supply Al mass Al mass amountconcentration concentration (cc/min) (%) ratio Comparative 0 12.12 1example Example 5.0 11.21 0.92 12.0 9.95 0.82 20.0 8.36 0.69 30.0 5.790.48 40.0 6.08 0.50 50.0 5.82 0.48 60.0 6.04 0.50

TABLE 16 Changes in amount of abrasive stuck in test piece with changesin water supply amount (iron) Water supply Al mass Al mass amountconcentration concentration (cc/min) (%) ratio Comparative 0 12.35 1example Example 3.0 11.57 0.94 8.0 10.40 0.84 16.0 10.04 0.81 25.0 8.50.69 40.0 6.82 0.55 60.0 5.21 0.42

TABLE 17 Changes in amount of abrasive stuck in test piece with changesin water supply amount (acrylic) Water supply Al mass Al mass amountconcentration concentration (cc/min) (%) ratio Comparative 0 2.02 1example Example 1.0 0.79 0.39 6.0 0.71 0.35 10.0 0.75 0.37 20.0 0.710.35 30.0 0.68 0.34 40.0 0.69 0.34 50.0 0.73 0.36 60.0 0.67 0.33

TABLE 18 Changes in amount of abrasive stuck in test piece with changesin water supply amount (epoxy glass) Water supply Al mass Al mass amountconcentration concentration (cc/min) (%) ratio Comparative 0 2.49 1example Example 3.0 1.43 0.57 6.0 1.42 0.57 10.0 1.54 0.62 20.0 1.430.57 30.0 1.61 0.65 40.0 1.49 0.60 50.0 1.59 0.64 60.0 1.61 0.65

It was confirmed from the above results that sticking or lodging ofabrasive decreases when a liquid was supplied compared to when blastingwas carried out without supplying water.

Sticking or lodging of abrasive can be reduced even when processing iscarried out by a known wet blasting method. However, because the cutamount decreases in known wet blasting compared to dry blasting asdescribed before, good processing performance and the reduction ofsticking or lodging of abrasive cannot be achieved by wet blasting atthe same time.

In contrast to this, the method of the present invention has theunexpected effect of being able to improve the cut amount compared notonly to conventional wet blasting but also to blasting without involvingwater supply as described above and prevent sticking or lodging ofabrasive at the same time.

(4) Results of Measurements of Amount of Consumption and Particle Sizeof Abrasive

Test pieces made of SUS304 were subjected to blasting at an ejectionpressure of 0.5 MPa using zircon beads (“FZB-60” manufactured by FujiManufacturing Co., Ltd., average diameter: 200 μm) as the abrasive bythe blasting method of the present invention, which used the blastnozzle shown in FIG. 2A (example) and, a dry blasting method, which useda known blast nozzle (having a structure obtained by removing the liquidintroduction path 88 from the blast nozzle shown in FIG. 2A)(comparative example). The amount of consumption of abrasive wasmeasured and the condition of particles of the abrasive was observedafter the blasting.

The ejection was carried out in a continuous manner (in an abrasivecirculating-type blasting apparatus shown in FIG. 1). The weight of theabrasive introduced into the abrasive tank of the blasting apparatusbefore starting the measurement and the weight of abrasive recoveredwere measured, and the decrease in weight was evaluated as the amount ofconsumption.

The blasting time was 45 minutes and water was introduced at a rate of 6cc/min in the blasting method of the present invention.

The results of measurements of the amount of consumption of abrasive areshown in Table 19 and the conditions of the particles of the abrasiveafter use are shown in FIG. 20.

TABLE 19 Results of measurements of amount of consumption of abrasiveExample Comparative (after drying) example Water supply amount 6 cc/min0 cc/min Continuous ejection method −130.0 g −225.3 g

It was confirmed from the above results that the blasting method of thepresent invention could reduce the amount of consumption of abrasivecompared to the known dry blasting method.

According to the results of observation of the particle size of therecovered abrasive (see FIG. 20), the abrasive used in the dry blastingmethod underwent rapid crushing compared to the abrasive used in theblasting method of the present invention and therefore had a smallerparticle diameter. In this respect, it was confirmed that there was alarge difference in the consumption of abrasive.

(5) Measurement of Surface Temperature of Workpiece

(5-1) Temperature Measurement with Thermocouple

Zircon beads (“FZB-400” manufactured by Fuji Manufacturing Co., Ltd.,particle diameter: <0.05 mm) as an abrasive was ejected onto copperplates with a size of 15 mm×15 mm×0.5 mm at an ejection distance of 100mm and an ejection pressure of 0.3 MPa or 0.5 MPa, and the changes intemperature of the copper plates were measured.

The temperature measurement was carried out by attaching athermocouple-type thermometer to a backside of each copper plate so thatthe change in temperature could be read, and the abrasive was ejectedfor several seconds using the blast nozzle shown in FIG. 2A while thewater supply amount was being varied. The highest temperature displayedwhile the abrasive was being ejected was employed as the measurementvalue. The results of measurements are shown in Table 20.

TABLE 20 Processing pressure 0.3 MPa 0.5 MPa Comparative Comparativeexample Example example Example Water supply 0 1.4 3.6 0 1.5 3.1 amount(cc/min) Temperature 54 36 26 56 42 29 (° C.)

It was confirmed from the above results that the blasting method of thepresent invention could significantly reduce the temperature rise of theworkpiece compared to a dry blasting method.

(5-2) Confirmation of Heat Generating State

The temperature measured in the above test was the temperature of thebackside of a copper plate as a processing object measured while theabrasive was being ejected for as fairly short a period as severalseconds, and it is expected that the temperature of the surface wherethe strike with abrasive occurs instantaneously rises to a level highenough to soften the surface of the workpiece.

Thus, the blasting method of the present invention and a dry blastingmethod were applied to paint stripping from PC (polycarbonate) resinproducts and deburring of PPS (polyphenylene sulfide) resin products andthe post-processing states were compared so that the difference insurface temperature of the workpiece between the blasting method of thepresent invention and the dry blasting method could be understoodinstinctively.

The paint stripping from the PC resin products was carried out byejecting a high-purity alumina abrasive (“FUJIRUNDUM WA #600”manufactured by Fuji Manufacturing Co., Ltd.) at a processing pressureof 0.4 MPa and a nozzle distance of 70 mm using the blast nozzle shownin FIG. 2A. The processing was carried out with a water supply amount of5 cc/min in the method of the present invention (example) and withoutsupplying water in the comparative example.

The deburring of the PPS (polyphenylene sulfide) resin products wascarried out by ejecting nylon beads (“FNB-0303” manufactured by FujiManufacturing Co., Ltd.) using the blast nozzle shown in FIG. 2A at aprocessing pressure of 0.4 MPa and a nozzle distance of 20 to 30 mm. Theprocessing was carried out with a water supply amount of 3 cc/min in themethod of the present invention (example) and without supplying water inthe comparative example.

The results of measurements of surface roughness of the PC productsafter the paint stripping are shown in FIG. 21, and the results ofmeasurements of surface roughness of the PPS products after thedeburring are shown in FIG. 22.

It can be understood from the processing results that the surfaceroughness of the resin product processed by the method of the presentinvention (see FIG. 21A and FIG. 22A) was lower than that of the resinproduct processed by the dry method of the comparative example (see FIG.21B and FIG. 22B) in either case. From these results, it is believedthat the surfaces underwent significant deformation caused by thermalsoftening in the dry blasting.

In addition, the surfaces of the resin products processed by the dryblasting had been burnt dark whereas no burning was observed on theresin products processed by the method of the present invention. In thisrespect, it was confirmed that the method of the present invention couldeffectively prevent the workpiece from generating heat.

Such burning occurs not only when resin products are processed but alsowhen products made of a metal such as aluminum are processed. The methodof the present invention can also prevent occurrence of burning in theprocessing of such metal products.

In addition, it took 11 to 12 seconds to carry out the paint strippingby dry blasting whereas the method of the present invention was able toreduce the time to 6 to 7 seconds. It was therefore confirmed that thepaint stripping efficiency could be improved when blasting was carriedout by the method of the present invention.

The same effect was observed not only in paint stripping from a surfaceof a resin base material but also in paint stripping from a surface of ametal base material such as aluminum alloy, magnesium alloy, zinc alloy,brass alloy or iron.

In the deburring, even burrs that could not be removed by dry blastingcould be removed by the blasting of the present invention. It wastherefore confirmed that the blasting of the present invention was alsoeffective in deburring.

The differences are believed to be due to the fact that the surfacetemperature of the workpiece rises until the coated film or burrs becomesoft enough to absorb the impact of strike of the abrasive and maketheir stripping or removal difficult in dry blasting, whereas thesurface of the workpiece is cooled and the coated film or burrs areprevented from becoming soft and remain hard (and thus brittle) enoughto be easily stripped or removed by strike of the abrasive in the methodof the present invention.

(6) Confirmation of Warpage Occurrence State

Almen strips (A strips) were processed using the blast nozzle shown inFIG. 2A and using a zircon shot (“FZB-425” manufactured by FujiManufacturing Co., Ltd. (Median particle diameter: 425 μm to 600 μm,average diameter: 513 μm)) as the abrasive.

The processing was carried out at processing pressures of 0.3 MPa and0.5 MPa for 20 seconds. The arc height value (the height to which thetest piece was curved) was measured at various water supply amounts andevaluated as “warpage.” The results of measurements are shown in Table21.

TABLE 21 Result of confirmation of warpage occurrence state Ejectionpressure Water supply amount (cc/min) Arc height 0.3 MPa 0 0.163 mmA 1.40.158 mmA 3.6 0.158 mmA 0.5 MPA 0 0.244 mmA 1.5 0.238 mmA 3.1 0.238mmA * The “A” in “mmA” indicates the use of an A strip.

It was confirmed from the above results that warpage of the workpiececould be slightly reduced when blasting was carried out by the method ofthe present invention.

DESCRIPTIONS OF REFERENCE NUMERALS

-   1 Blasting apparatus-   2 Cabinet-   21 Processing chamber-   3 Abrasive tank (cyclon)-   5 Dust collector-   6 Exhauster-   7 Flow control valve-   8 Blast nozzle-   81 Body-   82 Nozzle tip-   82 a Conical inner surface-   83 Rear nozzle-   84 Abrasive introduction port-   85 Abrasive introduction chamber-   86 Compressed gas flow path-   88 Liquid introduction path-   88 a Distal end (of Liquid introduction path)-   91 Abrasive recovery pipe

1. A blasting method in which an abrasive is ejected together with acompressed gas onto a workpiece through a blast nozzle comprising thestep of: introducing a liquid into the blast nozzle and atomizing theliquid by causing the liquid to strike with the compressed gas flowingthrough the blast nozzle or the compressed gas ejected from the blastnozzle, and ejecting the atomized liquid together with the compressedgas and the abrasive, an amount of the liquid introduced into the blastnozzle being 0.06 cc/min to 150 cc/min.
 2. A blasting apparatus forejecting a stream of compressed gas supplied from a compressed gassupply source and an abrasive from a blast nozzle as a mixed fluidcomprising: a liquid introduction path provided in the blast nozzle,having one end communicable with a liquid supply source and an other endopened in a compressed gas flow path in the blast nozzle or at anejection port of the blast nozzle, the liquid introduction path beingconfigured to cause a liquid introduced from the liquid supply source tostrike with a stream of compressed gas flowing through the blast nozzleor a stream of compressed gas ejected from the blast nozzle to atomizethe liquid, and a flow rate control means provided between the liquidintroduction path and the liquid supply source.
 3. The blastingapparatus according to claim 2 wherein the blast nozzle is asuction-type blast nozzle provided with a nozzle tip directed in theejection direction of a rear nozzle communicated with a compressed gassupply source, and with an abrasive introduction chamber communicatedwith an abrasive supply source between the rear nozzle and the nozzle,the blast nozzle being configured to create a negative pressure in theabrasive introduction chamber by ejection of a stream of compressed gasfrom the rear nozzle to suck an abrasive in the abrasive supply source,and eject the compressed gas and the abrasive as a mixed fluid, and theother end of the liquid introduction path is opened in a compressed gasflow path formed in the rear nozzle or in front of an ejection port ofthe rear nozzle.
 4. The blasting apparatus according to claim 3 whereinthe liquid introduction path is formed by a conduit insertedconcentrically in the compressed gas flow path provided in the rearnozzle, and the other end of the liquid introduction path is opened atthe ejection port of the rear nozzle.
 5. The blasting apparatusaccording to claim 2, further comprising a fixed quantity liquid supplymeans for supplying the liquid in the liquid supply source to the liquidintroduction path in a fixed quantity.
 6. The blasting method accordingto claim 1, wherein the abrasive is ejected at an ejection pressure of0.3 MPa to 0.5 MPa.
 7. The blasting method according to claim 1, whereinthe abrasive is a nylon bead, an alumina abrasive, a high-purity aluminaabrasive or a zircon grid.
 8. The blasting method according to claim 1,wherein an ejection amount of the abrasive is 2 g/min to 20 kg/min. 9.The blasting apparatus according to claim 2, wherein a mesh material isprovided in an opening at the other end of the liquid introduction path.10. The blasting apparatus according to claim 2, wherein the blastnozzle is a direct-pressure type blast nozzle, and the other end of theliquid introduction path is opened at a position where the ejection portof the blast nozzle is formed, or the other end of the liquidintroduction path is opened in a compressed gas flow path in a rearnozzle provided in a body of the blast nozzle or in a compressed gasflow path formed through a nozzle tip attached to a distal end of theblast nozzle.
 11. The blasting apparatus according to claim 3, whereinthe nozzle tip is constituted to have two divided nozzle tips coaxiallyand sequentially arranged in a longitudinal direction and a vent isformed at an interface between the nozzle tips.
 12. The blastingapparatus according to claim 10, wherein the nozzle tip is constitutedto have two divided nozzle tips coaxially and sequentially arranged in alongitudinal direction and a vent is formed at an interface between thenozzle tips.